Tropical cyclone rapid intensification: patterns related to geography, time of season, and storm characteristics

I examined best track data on tropical cyclones in the Atlantic from 1950 to 2009 to determine how the tendency to rapidly intensify varied among broad sub-regions of the study area, times within the season, and times when the storm displayed different characteristics. Two definitions of rapid intensification were employed, wind speed increases of 15 kt/24 h and 30 kt/24 h, which ended up showing similar patterns.

Probability of a cyclone beginning rapid intensification was greatest in the Gulf of Mexico and lowest in the northeast Atlantic. It did not display a peak during the early September peak of overall cyclone occurrence. Cyclones were most likely to begin rapidly intensifying immediately after cyclogenesis, and at that time were most likely to do so if they displayed 35 kt initial wind speeds. Cyclones of > 1 d age showed peaks of intensification onset at 30 kt and 70 kt. Intensification was most likely to begin when winds were unchanged over the preceding 6 h, and when central pressure had dropped by 1 or 2 mb over 6 h. In three time zones, intensification of 15 kt/24 h appeared most likely to begin shortly after midnight, and least likely shortly before midnight. I discuss the possibility that spurious patterns could have resulted from overlapping influences of explanatory variables, or from biases in procedures of storm observation.